The invention relates generally to surface treatment and, more particularly, to methods for providing corrosion and abrasion resistance to a surface of a ferrous material.
Many of today""s earthmoving, agricultural, recreational, and military machines use tracks for propulsion. The track typically includes numerous track links chained together, each track link having metal or rubber pads that contact and grip the ground. Adjacent track links are generally joined to one another at track joints by bushing assemblies. A bushing is inserted between a pin and a bore on the track link through which the bushing passes. As the tracked machine moves, the track links move around a portion of a sprocket wheel as the individual links rotate around the pin and bushing. To resist fracture under stress and withstand impact, the bushing is typically made from a plain carbon or medium alloy steel.
Oil or grease is typically used as a lubricant in the bushing assembly. The oil may be confined by a polymeric seal located between the end surface of the bushing and the inner surface of the track link bore. Because the polymeric seal slides against a portion of the end surface of the bushing as the track moves, the end surface of the bushing contacting the polymeric seal is typically ground and polished to provide a smooth sealing surface against which the polymeric seal can slide. The ground sealing surface, however, still abrades the polymeric seal. Furthermore, the track operates in a corrosive and abrasive environment that can exacerbate grooving of the end surface of the bushing and polymeric seal. Grooving can result in oil leakage and subsequent seizing and failure of the track.
Surface treatment by thermochemical diffusion processes are known to impart abrasion resistance to the surface of steels, for example, plain carbon or medium alloy steels, without affecting the tougher, impact-resistant underlying material. In particular, nitrocarburization processes, such as disclosed in U.S. Pat. No. 5,102,476, are known to provide increased wear and corrosion resistance to steel surfaces. The disclosed nitrocarburization process introduces nitrogen and carbon into the surface of steels to produce a xe2x80x9cwhitexe2x80x9d or xe2x80x9ccompoundxe2x80x9d layer. The compound layer, depending on the steel alloy and the diffusion atmosphere, contains varying amounts of xcex3xe2x80x2 (Fe4N), xcex5 (Fe2-3N), cementite, carbides, and nitrides. Similarly, nitriding introduces nitrogen into the surface of steel to form a hardened, abrasion resistant layer.
While the nitrocarburized or nitrided layer provides some corrosion and wear resistance, its surface still abrades the polymeric seal thereby allowing abrasives and corrosives to get between the polymeric seal and the end surface of the bushing to cause further grooving. Grinding of the nitrocarburized or nitrided layer is generally avoided to prevent damage of the compound layer.
Thus, there is a need to overcome these and other problems of the prior art and to provide a surface and a method for treating a surface that avoids grooving. The present invention, as illustrated in the following description, is directed to solving one or more of the problems set forth above.
In accordance with one aspect of the present invention, a method is provided for treating a surface of a first component, wherein at least a portion of the surface of the first component contacts a surface of a second component. The method includes forming a compound layer at the at least a portion of the surface of the first component by a thermochemical diffusion treatment and isotropically finishing the at least a portion of the surface of the first component that contacts the surface of the second component.
In accordance with another aspect of the present invention, a method is provided for treating a surface of a track bushing wherein at least a portion of the surface of the track bushing contacts a polymeric component to form a seal. The method includes subjecting the surface of the track bushing to a thermochemical diffusion treatment to form a compound layer and isotropically finishing at least the portion of the surface of the track bushing that contacts the polymeric component to a surface roughness of Raxe2x89xa60.1 xcexcm.
In accordance with another aspect of the present invention, a track bushing is disclosed. The track bushing includes a surface, wherein at least a portion of the surface is isotropically finished and includes a compound layer.
In accordance with yet another aspect of the present invention, a track is disclosed. The track includes a plurality of track links, each of the plurality of track links including a bore at a first end and a second end. The track further includes a plurality of bushing assemblies, wherein the plurality of bushing assemblies join adjacent track links by residing in the bore at the second end of a first track link and the bore at the first end of a second track link. Each of the plurality of bushing assemblies includes a steel bushing having an isotropically finished surface, wherein the isotropically finished surface includes a compound layer and a pin that fits in the steel bushing. The track further includes polymeric seals that contact the isotropically finished surface of the steel bushing and an inside surface of the bore of at least one of the adjacent track links.